1. Field of the Invention
The present invention relates to a surface treatment method and apparatus therefor for liquid treating semiconductor wafers or other objects.
2. Description of the Prior Art
As is well known, various surface treatments with liquid chemicals such as etching, photo-resist film removal and water cleaning of wafers are carried out in production lines of semiconductor devices. For example, Japanese Patent Laying Open Gazette No. 52-150974 (1977) discloses an apparatus for executing these series of surface treatments automatically, wherein various treatment baths and a drier are arranged in a line and a transfer machine travelling along the line is provided. Cassettes holding a plurality of wafers are suspended by a handling mechanism of this transfer machine and successively dipped into baths of treatment liquids. Such a treatment sequence is followed automatically in response to command signals supplied from a controller consisting of a microcomputer and other components.
However, in such a conventional apparatus, because the take-in operation of the cassettes must be interrupted during replacement and addition of the treatment liquids in the baths, the cassette flow becomes intermittent, resulting in low processing efficiency.
In particular in some surface treatments such as in multistage surface cleaning processes, types, concentrations and temperatures of the cleaning liquids and further treatment periods and treatment orders must be differentiated according to the stage where the wafers are present in the production line. This results in various combinations of treatment conditions. Therefore, if all these treatments are carried out in a conventional apparatus, the treatment sequence must be changed from one to another after all treatments for one cassette are completed and then the next cassette is fed onto the treatment line. Therefore, the next cassette must wait for a while at a loader, resulting in a substantial decrease of the efficiency of the treatments as a whole.
Moreover, replacement of the treatment liquid must be carried out, taking several factors such as time lapse from the proceeding replacement and number of dippings of the cassettes into consideration. This control of treatment liquids has been managed manually or semi-automatically. Therefore, the lifetime of a new replaced liquid is disadvantageously consumed before the next cassette is dipped and the liquid must be replaced by new liquid. Moreover, insufficient control of treatment liquid causes deviation of the treatment quality of the wafers depending on the cassette in which the same is held, degrading uniformity.
These problems are caused not only in the surface treatment of semiconductor wafers, but in several other surface treatments such as surface treatment of the glass substrates of etching masks.